Linear hydraulic actuators of various forms are currently used in industrial mechanical power conversion applications. One common industrial usage is in construction equipment (e.g., excavators, backhoes) in which the linear action of a hydraulic piston is converted to rotary motion about a joint.
In certain applications, such as the actuators used for heavy equipment operation, increased actuation speed, wide ranges of motion, efficiency of fluid power usage, and ease of maintenance are desired. However, despite their widespread use, it can be difficult to provide such characteristics in typical heavy equipment applications of linear hydraulic actuators, e.g., on the arm and bucket of an excavator.
Rotary hydraulic actuators of various forms are also currently used in other types of industrial mechanical power conversion applications. This industrial usage is commonly for applications where continuous inertial loading is desired without the need for load holding for long durations, e.g., aircraft using rotary vane actuators on flight control surfaces, and applications where load holding is not an issue, e.g., backhoes using hydraulic motors to pivot the house or boom horizontally relative to the undercarriage. The designs of such actuators, however, do not scale well to provide the combinations of power-to-weight ratios, field-serviceability features, stiffnesses, holding capacities, torque-to-weight ratios, slew rates, energy efficiency, and/or the field-serviceability typically expected by heavy equipment operators for use elsewhere in their equipment, e.g., actuation of vertical joints of the arm.